Neural recording and neurostimulation are categories of medical devices that are used to interact electrically with tissue. In the case of neural recording, physiological measurements are performed of neurological tissue that can diagnose, or treat, a patient. In the case of neurostimulation, electric charge is transferred to the tissue in order to create a therapeutic outcome, or to generate a diagnosis. Neural recording and neurostimulation devices are used today in the cochlea, the retina, the peripheral nervous system, the spine, the brain, and other parts of the body.
In a particular application where both neural recording and neurostimulation are utilized, conductive electrodes are placed in contact with deep brain structures in order to treat certain neurological conditions. In the case of stimulating the Pedunculopontine Nucleus, for example, as described in U.S. Pat. No. 6,356,784, the therapy can treat the symptoms of Movement Disorders such as Parkinson's disease. In the case of stimulating Brodmann Area 25, for example, as described in U.S. Pat. No. 7,346,395, the therapy can treat the symptoms of Mood and Anxiety Disorders.
Generally, neural recording is performed in deep brain structures by surgically inserting conductive electrodes and amplifying neurological signals using external electronic equipment. Neurostimulation, is performed by surgically implanting conductive electrodes in the target, and using an implantable pulse generator to apply electrical signals to the conductive electrodes.
In some cases, such as described in U.S. Pat. No. 6,016,449, a system has been developed where both neural recording and neurostimulation functions are available in a single, long term implantable, device.
In most techniques, the electrodes used for neural stimulation that are placed in contact with tissue have been metallic, cylindrical, with very sharp distal ends. In most cases, they only contain one microelectrode, which severely limits the amount of physiological information that can be collected from the patient.
In other techniques, the electrodes used for neurostimulation that are placed in contact with tissue have been metallic, cylindrical, and relatively large in size (e.g., 1.27 mm in diameter and 1.5 mm in length). In most cases, there are four or eight cylindrical electrodes placed on a common axis. The stimulation methods are generally invasive, such as with the electrodes used in Deep Brain Stimulation, and the electrode lead is generally attached implantable pulse generator.
Furthermore, advances in micromachining technology have developed whole new applications for medical devices, and in particular, implantable devices such as for the treatment and diagnosis of neurological disorders.
Advances in the imaging of tissue have elucidated the function and anatomy of brain and nervous tissue, permitting the development of new therapies which include electrical stimulation methods. A number of research groups have reported on different approaches for imaging methods, and the construction of implantable devices to deliver therapies. The imaging methods are generally extra-corporeal, and involve large and/or sophisticated equipment such as Magnetic Resonance Imaging systems.
One of the great challenges for clinicians delivering electrical stimulation therapy is in localizing the correct location for electrode placement, and then confining the stimulation field to the appropriate anatomical target to deliver the therapy, without inducing side effects. Clinicians generally combine pre-operative navigational planning derived from Magnetic Resonance Imaging and/or Computed Tomography scan imaging systems, with intra-operative microelectrode recordings of electrophysiological phenomenon to find and locate the optimal target.
Volumes of anatomical interest are commonly found using microelectrode recording techniques which involve invasively inserting metal tips to find the area of interest by its electrophysiological activity. This may be uncertain, time consuming, and repetitive insertions may be hazardous to patient health.
Unfortunately, there are several limitations to current practice including uncertainty, discomfort for the patient, and a heavy financial burden to deliver the therapy. These factors can render the therapy less attractive to clinicians, patients and payers.
It would be a very useful advancement in the art of neural recording and neurostimulation device technology and in the practice of functional neurostimulation if the same device could image a volume of brain tissue, and stimulate the same volume of tissue with precision and safety.
There are many other medical applications for the present device, such as detecting malignant tissue within healthy tissue.